Vehicle cargo compartments for transporting bulk materials such as dirt, sand, grass clippings and the like are often covered with a canopy, also called a tarpaulin or tarp, during travel in order to avoid the blowing out part of the load and thus creating a hazardous condition on the highway or contaminating the surroundings, or to prevent the load from getting wet. The tarp needs to be held in place tightly to avoid being dislodged by the wind. Then the compartment needs to be uncovered to unload and load the bulk materials. The repeated covering and uncovering of the compartment can be time-consuming.
Over the years, many automated covering systems have been developed such as the one disclosed in Odegaard, U.S. Pat. No. 4,834,445 incorporated herein by reference, which uses a hydraulic motor to drive the deployment of the sheltering canopy off of a winding roller and over the cargo compartment, and to drive the retraction of the canopy back onto the roller. One advantage of hydraulic motors is that they are easily controlled in the forward and reverse direction by adjusting the pressure of the fluid present. Hydraulic systems however may not be favored in some situations where leaking hydraulic fluid can contaminate other systems or cargo. In addition, hydraulic motors can have complex controls. Systems such as that disclosed in UK Patent GB 2410 926 B Rogerson, can be costly to manufacture, install, and maintain.
Some canopy systems use air driven motors. However such systems can be difficult to install and maintain due to lack of familiarity by operators. Further, some canopy systems are designed to tap into the existing vehicle air system operating the vehicle air brakes. Problems with the canopy air system can therefore lead to more serious problems involving the vehicle brakes.
Some systems use electric motors driven by the vehicle electrical system. Often to reduce the cost of the system, the type of electric motor selected can fall within a fairly narrow range of performance characteristics. This can be problematic in the cargo canopy field which is subject to changing conditions, harsh environments and rugged treatment. For example the canopy mechanism can be impeded by obstacles protruding from the cargo or the accumulation of rust or debris throughout its various components. Further, electrical systems operating in a hot, desert environment may tend to overheat more quickly then one operating in a cooler environment. Although more rugged electric motors are available, they tend to be more costly. Thus, mechanical systems which work in a seemingly similar field such as retractable awnings may not provide any useful guidance for designs in the cargo canopy field.
In some systems there is a dedicated motor to drive deployment actions and an additional separate motor to drive retraction actions.
Some canopy retracting mechanisms previously available are prone to erratic operation due to misalignment of canopy edges, uneven stretching of the canopy fabric, lack of synchronization between driving motors or the jamming of pulling and guiding components. In addition, as material is wound upon a roller or spool its effective diameter changes due to the material already wound on the spool. Thus, it can be difficult to predict the amount of material taken up for any given rotation. This can lead to uneven synchronization of motors, uneven tensioning on the material which in turn can lead to misalignment or other erratic operation. Therefore, in some canopy systems the deploying and retracting motors need to be well balanced and relatively precise in order to assure a smooth operation of the mechanism under the rugged, all-weather conditions typical for cargo vehicles. For stability and exactness of alignment, prior mechanisms have been proposed which require complex boom and lever structures as disclosed in PCT International Publication WO 2005/005186 Hines.
The instant invention results from efforts to address one or more of the above problems with prior cargo canopy systems.